Combination catalytic cracking process



Nov. 4- 1958 w. G. REYMOND I 2,859,172 COMBINATION CATALYTIC CRACKINGPROCESS Filed Oct. 26. 1954 1 5 DISTILLATION Y ZONE 2 CATALYTIC 3 r 6}f: "CRACKING a ZONE T 4 FRACTIONATING 32 ZONER 2 3h. I

GAS OIL LUBE RAFFINATE CYCLE o "5 F 28 RAFFINATE |5 RAFFINATE PHENOLHEAVY GAS -J Z QIL 53cm IO OIL CYCLE OIL AROMATIC EXTR CT EXTRACT 1INVENTOR.

WILLIAM G.REYMOND ATTO NEY United States Patent COMBINATION CATALYTICCRACKING PROCESS William G. Reymond, Baton Rouge, La., assignor to EssoResearch and Engineering Company, a corporation of Delaware ApplicationOctober 26, 1954, Serial No. 464,768

6 Claims. (Cl. 208-87) This invention relates to the refining ofpetroleum oils aromatic hydrocarbon types which are refractory tocracking. In another aspect, the invention includes a method forimproving the value of a virgin gas oil fraction of a petroleum oil forcatalytic cracking by substantially reducing or eliminating organiccompounds containing metals that normally are present in the gas oil.Furthermore, the invention includes provision for improving the qualityof the extract hydrocarbons obtained from extraction of a lubricatingoil distillate, making these bydrocarbons more suitable for catalyticcracking.

The basic feature of this invention concerns the solvent extraction ofvirginor cracked fractions of petroleum boiling in the gas oil boilingrange so as to upgrade these fractions for use as catalytic crackingfeed. The invention entails the use of selective solvents for aromatichydrocarbons, employing these solvents to efliciently remove metalcontaminants and refractory hydrocarbons from catalytic cracking feedstocks with substantially no loss of hydrocarbon constituents suitablefor cracking. This is achieved by employing at least two extractionstages, in one of which cracked fractions of petroleum are treated andin the other of which virgin fractions of petroleum are treated. Theheart of this invention entails the use of the total extract phase fromone of these extraction stages for the treating or extraction agentinthe other of the extraction stages. This innovation not only materiallysimplifies solvent recovery facilities but greatly improves theefliciency with which constituents are removed which are undesirable forcatalytic cracking.

In its most specific and :preferred form, the present inventionaccomplishes these objectives by integrating a lubricating oilextraction process with a catalytic cracking operation. In oneembodiment of the invention, a lubricating oil is treated in anextraction operation with a selective solvent for aromatic hydrocarbons.The total extract phase formed in this extraction step is then used tocontact catalytic cycle oil providing a first rafiinate product. Thetotal extract phase from this extraction of.

catalytic cycle oil is then employed to contact a gas oil which hasundesired organic compounds containing metal contaminants providing asecond rafiinate product. The

I combined rafiinate products resulting from these treatments includesubstantially all of the desirable constituents of the lubricating oilextract, cycle oil, and gas oil which are suitable for catalyticcracking while minimizing inclusion of detrimental metal contaminantsand refractory aromatic hydrocarbons. In another embodiment of thisinvention, the extract phase from extraction of a' lubricating oil isused to contact gas oil. The extract phase resulting is then used tocontact catalytic cycle 7 tivity and life of this catalyst.

. at an economically prohibitive cost.

the fact that the phenol acts as a selective solvent to re' 2 3 oil. Thecycle oil and gas oil rafiinate products are particularly suitable forcracking.

In these and other specific embodiments of the invention high molecularweight aromatic hydrocarbons present in the solvent extract phase of -aprior contacting step, serve to alter the nature of the gas oil andcycle oil ex traction so as to provide rafiinate products of improvedcharacteristics forcatalytic cracking feed.

As indicated, the present invention comprises arla tively complicated.combination of a variety of treating steps and refining processes. Inorder to lay a basis for fully understanding the nature and features ofthis invention, attention will be directed to several aspects. of thefield involved.

At the present time, the process of catalytic cracking is extensivelyemployed for converting high boiling portions of a petroleum crude oilto lighter boiling, commercially valuable products including gasolineand heating oils. The feed stock to a catalytic cracking unit ordinarilyconstitutes portions of 'a petroleum crude oil boiling above thegasoline boiling range or boiling above about 430 F. It is economicallydesirable to include the highest boiling fraction of a petroleum crudeoil attainable by the vacuum distillation of atmospheric reduced crude,and for this purpose, the feed to a catalytic cracking unit preferablyincludes constituents of the crude oil boiling up to about 1100 F., orhigher. As used herein, the term gas oil is used to identify thisportion of a crude oil boiling in the range of about 430 to 1l00' F. orsomewhat higher.

For some time it has been appreciated that inclusion organic compoundswhich contain certain metal contaminants. Among the organic metalliccontaminants present in heavy gas oil compounds of nickel, vanadium andiron are particularly objectionable in poisoning the catalyst usedduring catalytic cracking so as to decrease the selec- Recognizing thisproblem, there have been many suggestions aimed at minimizing metalcontamination of gas oils to catalytic cracking feed. In thisconnection, one possibility is that organic metal contaminants can bereduced by contacting the gas oil with a solvent such as phenol. Thecontacting of phenol and gas oil reduces these contaminants, but

move aromatic constituents of the gas oil as well as the undesiredcompounds containing metal contaminants. 'As a result, phenol contactingof gas oil conducted to eliminate organic metal contaminants of the gasoil provides a raflinate product in undesirably low yields. mainder ofthe gas oil is present in the extract phase from this contact togetherwith the organic metal contaminants removed from the raflinate. From thestandpoint of hydrocarbon types, it is desirable to use the extractportion of the gas oil for catalytic cracking feed as well as theraflinate portion. It is apparent therefore that this process does notprovide the desired objective of selectively separating the organicmetal contaminants from the gas oil usable as catalyticcracking feed.

A basic feature involved in the present invention is thev discovery thata selective solvent for aromatic hydrocarbons can be used to selectivelyextract organic metal feed. This is made possible by inclusion of highmolecular weight aromatic hydrocarbonsin the selective solventgas oilextraction system. The included high molecular,

weight aromatic hydrocarbons serve to displace compo- This results from.

The renents of the gas oil normally extracted by fresh solvent alone.Another-feature of this invention is the discovery that these highmolecular weight, aromatic hydrocarbons actually serve as a solvent forthese organic metal .constituents. Consequently, larger reduction ofthese contaminant-sis realized.

' It-hasbeen' found that the high molecular weight aromatic compoundspresent'in the extract phase of a catalytic cycle oil extraction processor alubricating oil extraction process are uniquely adapted to providethe above function. Consequently, ,one aspect of the present inventionentails the contact of a'heavy gas oil with a selective solvent in thepresence of aromatic hydrocarbons obtained from heavy cycle oil derivedfrom a catalytic cracking process or in the presence of aromatichydrocarbons derived from a lubricating oil. It is a particular featureof this invention that the desired-aromatic hydrocarbons are derivedfrom cycle oil or lubricating oil by solvent extraction, using theextract phase resulting from this contact as a selective solvent-for gasoil extraction with use of the resulting extract phase in subsequentextraction steps, if desired.

'The principles of this invention are illustrated in the accompanyingdrawing, which illustrates in diagrammatical form a flow plan embodyinga specific embodiment of the invention.

Referring to the drawing, the processing steps involved in the practiceof this invention are illustrated. The numeral 1 designates a catalyticcracking zone. The operation conducted in zone 1 may constitute anydesired type of catalytic cracking operation. Thus, the catalyticcracking may constitute the fixed bed type of cracking, moving bed typeof cracking, or fluidized catalytic cracking. In each of these types ofoperation, any of the various Well known cracking catalysts may beemployed. Generally, such catalysts are'the metal oxide types andpreferably include silica-alumina, silica-magnesia, or silica-gelpromoted with metal oxides" which are adsorbed thereon. Typical crackingconditions are at temperatures in the range of about 750 to 1050 F., andpressures ranging from atmospheric to somewhat above atmosphericpressure. The catalytic agent employed is regenerated intermittently orcontinuously in order to restore or maintain the activity of thecatalyst.

Inv accordance with this invention, a particular catalytic cracking feedstock as derived in the manner described hereinafter is introduced tocatalytic cracking zone 1 through line 2. For the present, it issufficient to note that the feed to catalytic crackingzone 1 generallyincludes the fraction of a crude oil boiling within the range of about430 to 1100 F. or higher. For typical operation, catalytic cracking ofthis feed stock would result in con- 800 F. may be removed from thelower sidestream with-,

drawal 7. Heavy residual. fractions of the vcatalytically crackedproducts are removed from the bottom of the fractionator through line 8.Bottoms withdrawal stream 8 wil include the highest boiling constituentsof the cracked products including hydrocarbons boiling up to about 1100F. or somewhat higher. In the event that powdered catalyst is employedin the catalytic cracking zone 1, some catalyst will be entrained in thebottoms Withdrawal. In this casethe product of line 8 may be device. Araflinate phase may then he recovered from subjected to a clarificationor settling operation in order to segregate the hydrocarbons 'fromcracking catalysts. The product of this operation is commonly calledclanfied oil and the stream of line 8 wil be so designated 1 preferablyemploys both of these products as combined,

in line 9 of the drawings and designated by the term cycle oil.

It is well known that cycle oil of the character identified is morerefractory than virgin catalytic cracking feed stocks of the sameboiling range and consequently constitutes relatively poor catalyticracking feed stock.

Cycle oil particularly includes refractory, high .molecthv lar weight,aromatic hydrocarbons which, if recycled to a catalytic crackingoperation, cause excessive .forma-.

tion of undesirable gas, .coke and .tar during-catalytic; cracking. Theconstituents of cycle oil whichare ,par-

ticularly objectionable for cracking are high molecular.

weight, aromatic hydrocarbons. The aromatic ,hydrocarbons present incycle oil include polynuclear aromatic hydrocarbons and condensedringaromatic hydrocarbons.

The condensed ring aromatic hydrocarbons are particularly undesirablefor inclusion in catalytic crackingfeed stock. As will be seen, theprocess .of this invention.

provides a means for improving cycle oil for catalytic cracking byelimination of these undesirable aromatic hydrocarbon types. 4 1

In accordance with the illustrated embodiment of .the

.invention, the cycle 'oil is contacted with the :extract l phase of alubricating oil extractionprocess. This-:ex-

tract phase may be obtained from the process illustrated at the left ofthe drawing occurring in the extractionzzone In zone 12, alubricatingoildistillat'e constituting the fraction of a crude oilboiling in'the range..of:about* 500 to 1100 F. is contacted with aselective solvent adapted to selectively extract aromatic constituentsof"- the lubricating oil. Phenol is oneof the selective solvents whichmay be employed, although other solvents maybe employed such asfurfural,nitrobenzene, aniline,

cresol, etc. Anti-solvents or solventmodifiers may he used andconventionally are used in conjunction with these solvents for theextraction of a lubricating oil. For

example, in the case of phenol, about 1 to 15% or some? what higherpercentages of water are preferably mixed" with the phenol or separatelyinjected during extraction, to provide .the best extraction results.stood therefore, thatthe lubricatingoil extraction process conducted inzone 12 may constitute any desired type i As diagram- I of selectivesolvent extraction operation. matically illustrated, extraction can beconducted-byin troducing lubricating oil at'the lower portionofthe'extraction zone through line 13. The selective solvent; such asphenol, is introduced into the top of the illustrated extraction zonethrough line 1'4. The phenol will i move downwardly through theextractionzone countercurrent to an upwardly moving streamofflubricatin'g' oil; permitting extraction of constituents of thelubricating oil by the phenol during this contact. Perforated" plates,pack1ng,fetc., may be usedin the tower to aid this con- Alternatively,the extraction zone may be a' tac'ting. tank mixer-settler combinationora centrifugal extraction the uppermost portion of the tower andwithdrawn through line 15, the product of which upon dewaxing.

The extractphase re-.. moved from the bottom ofthe tower throughline.1'6'-L Will include the spent phenol solvent together with the,extracted Virgin aromatic constituentsof the lubricating constitutes afinished lubricant.

It isl to be under- In this extraction process, the solvent to oil ratiowill ordinarily be between about 0.5 to 1 and 3 to 1. When employedphenol, or phenoLwater mixtures as the selective solvent, a solvent tooil ratio of about 1 to 1 to 2 to 1 is particularly suitable. In thecase of phenol extraction, the extract phase of line 16 will primarilyconstitute spent phenol including aromatichydrocarbons extracted fromthe lubricating oil. In general, the extract phase, will constituteabout 60 to 95% (preferably 75 to 85%) phenol and about 40 to 5% ofhydrocarbons extracted from the lubricating oil. enton the amount ofwater injection, about 0 to of water'will be included in the extractphase.

This extract phase resulting from selective extraction of a gas oil toproduce high quality lubricating oil is usually of value as a catalyticcracking feed stock. The extracted hydrocarbons for the most partconstitute single nucleus aromatic hydrocarbons with substituted alkylradicals which make the compounds sufficiently parafiinic so that theycan be attractively subjected to cracking. In the past, after solventremoval, the extract hydrocarbons from a lubricating oil extractionprocess have been used as catalytic cracking feed. The 'solventrecoveryoperation is a processing step which requires extensive and expensiverecovery facilities. It is one of the features of this invention topermit extraction of catalytic cycle oils without the addition of suchexpensive equip-' ment by making use of the lubricating oil extractionprocess in a novel and inexpensive manner.: This is achieved inaccordance with this invention by employing the lubricating oil extractphase as the extraction agent for catalytic cycle, oil. Incidentalquality improvement is realized for lubricating oil extract as acatalytic cracking-feed.

For this purpose, the totalextract phase from the lubricating oilextraction is contacted with the cycle oil of line 9. This' may becarried out in any kind of extraction zone which may be an extractiontower 24 similar in:

Thus, the cycle oil will nature to extraction tower 12. be introduced toa lowermost portion of tower 24 through line 9 while lubricating oilextract phase will be introduced to the top'of'tower 24 through line 16.Cycle oil will flow upwardly through the tower countercurrent todownwardly moving portions of the lubricating oil extract phase. l l 1This contacting results in displacement of lubricating oil constituentsfrom the phenol solvent by cycle oil consti'tuents. In particular, itappears that condensedring aromatic hydrocarbons present in the cycleoil are more soluble in the solvent than the extracted lube constituentsin the lubricating oil extract phase. Therefore, these extracthydrocarbons are displaced from the phenol phase. It has been found thatsubstantially all of the lubricating oil constituents can be recoveredfrom the lube extract phase so as to be removable as a rafiinate productfrom the top of tower 24 through line 25. This raffinate product willalso include constituents of the cycle 'oil suitable for catalyticcracking.

The extra t phase formed in tower 24 is removed as a bottoms productthrough line 26. This extract phase. will-include most of the phenoloriginally introduced to In addition, dependtower 27 Preferably'thecycle oil extract phase is used in amounts of about 125 to 225% based onthe-gasoil.

feed. The virgin gas oil of line 10 may constitute, the gas oilfractions of a crude oil boiling above about 430 F. The presentinvention is of particular application to gas oils in the higher boilingrange up to 1150 F., or somewhat higher in which higher concentrationsofor-- ganic metal compounds exist. As indicated, such gas oils arecharacterized by inclusion of organic compounds containing metalcontaminants such as nickel, vanadium I and iron. These metalliccompounds may be present in amounts of about 0.00002 to a 0.001% orsomewhat higher. The process of this invention is of application to suchgas oils in permitting removal of the metalcontaminants referred to.

In tower 27, contact of gas oil with the cycle oil extract phase resultsin the selective removal of metallic contaminants from the gas oil.Since the solvent present in the cycle oil extract is essentiallysaturated with high molecular weight, condensed ring aromatichydrocarbons, extracted from cycle oil, substantially none of the gasoil is taken up by solvent in extraction tower 27." As a result, therafiinate product withdrawn from tower 27 through line 28 comprises thehydrocarbon composition of the heavy gas oil introduced to the towerthrough line 10, with the substantial exclusion of the inants originallypresent in the gas oil.

The extract phase removed from tower 27 through line 29 will constitutespent phenol solvent together with highly aromatic hydrocarbonsextracted from cycle oil and metal contaminants removed from gas oil.Solvent tower 12 through line 14 and will include aromatic hydrocarbons'extracted primarily from the cycle oil. In

general, the cycle oil extract will include about 40 to 90% (morenarrowly, to phenol, and about 0 to 15% water, assuming that water ismixed with the phenol solvent during extraction, This cycle oil extractis em-- ployed to contact a heavy gas oil in extraction zone 27' whichmay ,be'a tower, a tank mixer-settler combination, or a centrifugalextraction device. In the illustration, a tower is depicted.

In accordance with this invention, the cycle oil extract phase of' line26 is contacted with a virgin gas oil introduced to thesystem throughline 10 for treatment in may be recovered from this extract phase andthe purified solvent can be recycled to line 14 constituting the phenolfed to tower 12. The concentrated aromatic hydrocarbons segregated inthe extract phase are valuable for many purposes.

The raffinate products of line 25 and 28 are combined in line 30 andpassed to distillation zone 31. Fractionation zone ,31 is operated topermit removal of phenol through line 32 and to permit removal ofhydrocarbon constitutents' of the combined rafiinates through line 33.The phenol recovered through line 32 may be recycled to the systemthrough line 14 of extraction tower 12. The hydrocarbon products of line33 are then employed as the feed to catalytic cracking zone 1 suppliedthrough line 2. In order to establish the novel and advantageousfeatures of this invention, reference will be made to exemplary datashowing the particular advantages of the multi-stage contactingdescribed.

In order to demonstrate the operation of the first two stages of theprocess described, conducted in extraction zones 12 and 24, two phenolextraction units of a lubricating oil refining plant were converted tothe processing principles of this invention. In one of the phenolextrac- Gravity, API 26.5-27.5

Viscosity, SSU/210" F. 39-42 Aniline point, F. 185-195 Diesel index -149-54 This distillate was treated with phenol in a counter.- currentextraction tower providing about 5 theoretical stages. The feed rateswere about 12,300 B./S. D. of phenol and about 7,450 B./S. D. of lubedistillate to pro vide a phenol treat of Water injection was main tainedduring extraction to "provide a total injection metal contam- A typical7 amount of about 2.5%, based on the phenol. The extractiontemperaturewas about-145 F.

Theextract phase obtained from this operation, constituted 84% penol; 2%water, and 14% hydrocarbons extractedfrom the lubricating oil feed.Thehydrocarbon constituents of the extract phase were primarilymono-nuclear aromatic compounds having substantial alkyl side chainsubstitution. Phenol'was separated from a portionof this extract phaseand it was found that the 8 treat expressed as the ratio of extractphase-to cycle oil. About 5 vol. percent water, based on theextract-phase; was injected during extraction. The temperature mainvol.percent based on total oil feed. The rafiinateprod hydrocarbonconstituents of the extract phase had the 1; uct had the followinginspections: following inspections: Gravity API 303 Gravity, .API 16.8-Viscosity, SSU/210 F. 41.3 Viscosity, SSU/2'10 F. 48.5 Silica gelanalysis: 7 Silica gel analysis: v Aromatics, wt. percent 25.8Aromatics, wt. percent 69.9 Paraifins, wt. perceent 74.2 Parafiins,.wt.percent 30.1 Conradson carbon, wt. percent 0. 11 Conradson carbon, wt.percent 0.3 Aniline point, F. 205.7. Aniline point, F. 130 Diesel index62.3 Diesel index 22 no Distillation, mm. Engler: Distillation, 10 mm.Engler: I. B. P., F 321 I. B. P.', 'F.' 366 5% 390 5% 411v 50% 483. 50%490 90% 576 n 584 For comparative purposes significant data includingThe economical disposition for these hydrocarbons is to that of theforegoing tests are collected'and reproduced catalytic cracking feed.Consequently, .in normal operas Table I below:

Table 1 Column 1 Column 2 C0lumn3 Column 4 Column 5 Column'fi" Raflinatefrom V Blend of Blendoi' Fresh Phenol Hydrocar- Extract and Extract andCycle Oil Extraction of hen Extract Cycle Oil Cycle Oil Raffinate- FeedCycle Oil at from Lube InFeed Raffinate 90%treat, 6% Oil Prop. In Prod.

1120 Prop.

PI 19.1 :5 16.8 18.8 30,8 30. SSU/210 F 41. 8 39.1 48.5 42.6 40. 6 41.Aromatics, Wt. percent" 46. 4 11. 2 69.9 49. 7 25. 9 25. Paraifins, Wtperce t 53.6 88.8 30.1 50.3 74.1 74. Aniline F 159 220 130 ConradsonCarbon content,

Wt. percent; 2. 5 0.3 0. 1. Diesel Index 30 7s 22 2e 66 62. 3

ation, after removal of the phenol in phenol recovery facilities,extract is sent to catalytic cracking feed In accordance with onefeature of this invention, the desirable portion of the hydrocarbonextract is recovered as rai-finate from the extract phase when theextract phase is contacted with cycle oil. Thequality of the hydrocarbonextract as catalytic cracking feed is accordingly improved. Thisoperation was conducted in the second of the phenol extraction unitsemploying a catalytic cycle oil having the following inspections:

This cycle oil was. contacted with the lubricating oil extract phase ina countercurrent treating tower having about 5 theoretical contactingstages. A cycle oil feed In this table, column 1 shows the inspectiousofthe catalytic cycle oil used in these tests. Column 2 shows the natureof a rafiinate product obtained by extract-' ing this cycle oil withfresh, or in other words, pur'e phenol for comparative purposes with theprocess. of this invention. Column 3 shows the inspections of thehydrocarbon portion of the lubricating oil extract phase referred to inthe foregoing tests. inspections of a blend of the extract ofcolumn 3and the. cycle oil of column 1 in the proportions used as feed in theforegoing tests of this phase of this invention; 85.9% cycle oil and14.1% extract. Column 5 shows a blend of the cycle oil raffinate ofcolumn 2.and the lubricating oil extract of column 3 in the proportionsresulting from the tests exemplifying this phase of' the invention;77.1% raffinateand 22.9% extract. Finally, column 6 shows theinspections of the raflfinate product resulting from the foregoing testsin accordance with the principles of this I invention.

of 6000 B./S. D: was maintained while introducing 7,020 B. /S, D. of theextract phase equivalent to 117%- The inspections given above must beconsidered in.

connection with the initial'characteristics ofboth the cycle oil feed totreating tower 17 (column 1) and the hydrocarbon extract feed to tower17 (column 3). Thus, as mentioned above, the raflinate product shown incolumn 6 includes constituents from each of these streams so that ineifect the raifinate product constitutes the seg-" regated portion ofboth the cycle oil and the lube' ex tract suitable for catalyticcracking feed. Comparing the inspections of therafiinate product toeither those. of the cycle oil feed or the hydrocarbon extract, it

Column 4 shows the 9 be observed that this product has substantiallybetter characteristics for catalytic cracking feed than either theuntreated cycle oil or the hydrocarbon extract. For

example, it will be observed that the untreated cycle oil had aConradson carbon content of 2.5 wt. percent and the hydrocarbon extract,0.3 wt. percent, while the raflinate product from tower 17 had aConradson carbon contentv of 0.1 wt. percent. Again the paraflin contentof the raffinate product was raised to 74.2 wt. percent as against avalue of 56.3 wt. percent for the untreated cycle oil and 30.1 wt.percent for the hydrocarbon extract. It is therefore shown thatoperation of the first two stages of the process illustrated in thedrawing results in substantially upgrading a cycle oil and a hydrocarbonlube extract, serving to materially improve their value as catalyticcracking feedstocks.

By a similar comparison of the inspections of column 6 with theinspections of column 5, it is shown that the rafiinate product of theextraction described is fully equivalent as a feed stock for catalyticcracking in comparison to a blend of lube oil extract and extractedcycle oil. This data, in combination with material balances, establishesthat a ratfinate product is obtained which segregates the hydrocarbonconstituents of the extract phase from lubricating oil together with theless aromatic portion of cycle oil much as though these were separatelyprepared and blended. In other words, the volume of lubricating oilextract hydrocarbons present in spent phenol from a lubricating oilextraction process is directly added to the volume of cycle oilrafiinate which would normally be obtained by the extraction of cycleoil with pure (or fresh) phenol at the same extraction conditions. Yetthis is achieved without necessity for distilling phenol from thelubricating oil extract phase, avoiding the expensive solvent recoveryfacilities ordinarily required for this at this step of the process.Again, this is achieved without any loss in quality of the product ascatalytic cracking feed.

These steps of the process illustrated in the drawing have additionalfeatures above and beyond those brought out heretofore. It is aparticular feature that lubricating oil constituents, normallycontaminated with metal compounds, are upgraded for catalytic crackingby substantial elimination of the metal contaminants. The metalcontaminants referred to include compounds of nickel, vanadium, and ironwhich result in poisoning of the cracking catalyst so as to seriouslydecrease the selectivity and life of the catalyst. As indicative of theproblem that exists, a typical lubricating oil fraction of a petroleumoil contained 0.58 p. p. m. of nickel. This lubricating oil wasextracted with phenol at a temperature of about 215 F. using a 200%treat of phenol and 2% of water. Separation of solvent from the extractphase provided segregated hydrocarbon constituents suitable forcatalyticcracking feed stock. However, extraction of lubricating oil ordinarilyresults in concentrating metal contaminants in .the hydrocarbon extractso that in this case the extract contained 1.16 p. p. m. of nickel.Heretofore the use of lube extract for catalytic cracking has beenseverely debited because of this metal contamination.

In the practice of this invention, however, a catalytic cracking feed isobtained, including the hydrocarbons present in a lubricating oilextract phase, which is substantially free of metal contaminants.Referring to the drawing, for example, the lube extract present in line16 is freed of metal contaminants in treating tower 24.

Metal contaminants are removed from tower 24 through line 26 togetherwith the extract phase of tower 24. The raflinate product of line 25,including the hydrocarbons originally present in the lube extract streamof line 16, is recovered for catalytic cracking free of metalcontaminants. In a typical case 90% removal of nickel was obtained bythis technique, providing a rafiinate product for catalytic crackingcontaining the extremely low nickel content of 0.02 p. p. m.

The data presented heretofore has concerned the preparation of a cycleoil extract phase as obtained in treating tower 24 illustrated in thedrawing. It has been shown that extract and raflinate phases of cycleoil, useful in the process of this invention, can be obtained bytreating cycle oil with a selective solvent by itself. It has also beenshown that particular advantages are secured if this is achieved bytreating cycle oil with the total extract phase of a lubricating oilextraction process. As pointed out, in either case a cycle oil extractphase is obtained constituting a major portion of spent solvent and aminor portion of aromatic hydrocarbons extracted from the cycle oil. Itis a particular feature of this inven-- tion that the total cycle oilextract phase be employed as an extraction agent for the treatment of avirgin gas oil 1 as conducted in tower 27 of the drawing.

in order to demonstrate the portion of the process conducted in tower27, experiments were conducted in which a cycle stock extract phasederived by contact of cycle oilwith lube oil extract phase as indicatedin the foregoing experimental results was contacted with a heavy gasoil. phenol and 30% oil. extract phase had the following inspections:

This cycle oil extract phase was employed to contact a gas oil havingthe following inspections:

Gravity, API

Viscosity, SSU/2l0 F 116 Conradson carbon, wt. percent 2.29 Sulfur, wt.percent 0.39 Nickel, p. p. m 2.1 Percent aromatics, wt. percent 39.9Percent paraffins, wt. percent 60.1

The cycle oil extract phase and gas oil were contacted in an extractionunit providing about 5 stages of theoretical contacting. The extractionwas carried out at a temperature of about 160 F. providing a phenoltreat of 114 volume percent based on the cycle stock extract phase. Thehydrocarbons present in the raifinate resulting from this contact hadthe following inspections:

Volume percent Yield of cracking feed 113 Gravity, APi 18.5 Viscosity,SSU/210 F 77.5 Conradson carbon, wt. percent 1.60 Nickel, p. p. m 0.3Percent aromatics, wt. percent 45.5 Percent paraffins, wt. percent 54.5

It will be noted from this data that contact of the gas oil with thecycle stock extract resulted in substantial elimination 'of metalcontaminants from the gas oil (87.0% removal) while permittingsubstantially complete recovery of all constituents of the gas oilsuitable for use as catalytic cracking feed., In fact, as indicated bythe 113% yield based on gas oil feed, the process was operative torecover the more paraffinic type hydrocarbons originally present in thecycle oil extract phase. This is The cycle stock extract phaseconstituted 70% The hydrocarbon portion of this .borne out bythefact-that the cycle oil extract phase used to contact the gas oil had anaromatic content of 84.6% while'th'e resulting extract phase had anaromatic content of about 94.5%.

A critical feature of this invention is the.use of separate contactingstages for the extraction of cycle stock and gas oil. border to show thebenefits of staged contact, reference is made to the following exemplarydata:

Ina first series of experiments; cycle stock and gas oil weremixed'together and contacted with a lubricating oil extract phase in asingle stage contacting operation. In a second, comparative series ofexperiments, the same catalytic cycle stock and the same gas oil wereseparately extracted in a two-stage operation. In this case, the cycleoil was first contacted with thelubricating oil extract phase'to form acycle oil extract phase. This'cycle oil extract phase was then contactedwith the gas oil in a second stage contacting operation. Theseexperiments established that substantially better extraction resultscould be obtained by the two stage contacting as comparedto the singlestage contacting. The unique advantage of plural stage contactingresides in the recovery of greater yields of raifinate product suitablefor cracking while securing equivalent or superior removal of metalcontaminants. To clearly show this, the tabulated data following waschosen for comparative single and double stage contacting adjusted tosecure the same amount of raflinate product. It will be noted thatsubstantially better nickel removal was obtained in the two stageprocess.

This data brings out the substantial advantages obtained from the stagedextraction process of this invention. The data shows that by employingtwo contacting stages as described in place of a single contactingstage, substantially better removal of nickel contaminants from gas oilis secured.

' Additional benefits also exist for this two stage process. In order toappreciate their significance, reference may be made to a typical plantsituation. Assuming the availability of lube oil spent solvent to be20,000 B./D. with a solvent content of 85 vol. percent, it can be seenthat a maximum of 19,666 B./D. of combined cycle stocksgas oils can beextracted in a single stage operation at a 75% solvent treat (defined asvolume of solvent per volume of total oil). In a two stage process, amaximum of 29,799 B./D. of cycle stocks-gas oils can be extracted at thesame 75% solvent treat. In this example, maximum permissible feed rateat constant treat is increased by about'l0,133 B.'/D. or 51%.

As described, this invention concerns extraction operations in whichvirgin and cracked gas oil fractions of a petroleum oil are separatelyextracted with a selective solvent for aromatic hydrocarbons whereinthetotal extract phase resulting from one extraction step is used in thesecond extraction step. Two of the most important applications of thisinvention have been brought out in the foregoing description and data.bone of these, fresh selective solvent is employed to'extract cycle oiland the'extract'phase from this extraction step is then used to extractvirgin gas oil. As established, the aromatic constituents'of the gas oilpresent in the cycle oil extract phase serve to improve removal of metalcontaminantsfrom the gas oil. The full advantages of this technique arealso achieved in the preferred embodiment of the invention illustrated.In this case, fresh solvent; is first-used to extract the lubricatingoil fraction'ofai virgin gas oil. The extractphase from thisoperation'is" then employed to extract" cycle'oil; Finally, the cycleoil extract phase is used 'to'extract gas oil: It'is apparent that theadvantages of this invention can be achieved toa lesser extent by use ofadditional contacting stages with the total extract phase of eachstagebeingused as the For example, in

extraction agent in successive stages. the case just described, the gasoil extract phase could be used in a subsequent extraction of virgin gasoil in order to-secure greater removal of metal contaminants 7 tractphase of a lubricating oil extraction step; and about 95% of the nickelcan be removed by using cycle oil extract phase. While this dataestablishes that the embodiment of the invention described is best.adapted for metal removal, it must be recalled that the invention isalso of utility for minimizing aromaticity of catalytic cracking feedstock.

Thus, for example, it is within the scope of this invention to employfresh solvent to extract lubricating, oil, using the lube extract phaseto extract virgin gas oil, andusing the gas oil extract phase to extractcycle oil Removal of metal contaminants fromthe gas oil in this sequenceof steps is somewhat inferior but the combination process does serve toprovide the objective of minirnizing the aromatic hydrocarbons incracking feed.

Again, if desired, fresh solvent can be used to extractgasoil with thegas oil extract phase being used to extract cycle oil in order torecover gas oil extract constituents suitable for cracking.

Among these variations of the invention, a preferred process entails useof the solvent extract phase from a lubricating oil'extraction processto extract gas oil at treats of about IOU-250% providing a firstrafiinate product and an aromatic extract phase.

extract phase is then used to extract cycle oil at treats of Thisaromatic about 50300% to provide a second raffinate product. Thecombined rafiinate products are of high quality for catalytic crackingfeed; Tests which have been carried' out show that this sequence oftreating steps serves to provide an over-all removal of nickelcontaminants of about 60-75% based on gas oil input. In this treatingcombination, it is particularly contemplated touse a portion of thelubricatingoil extract phase as a Wash for cycle oil raffinate, therebyfurther reducing the metal content of this stream. Volumetrically, theparatfinic part of catalytic cycle stock and essentially all of therecycle gas oil are recovered as catalytic cracking feed;

What is claimed is:

'1. An improved extraction process for the'preparation. of catalyticcracking feed stocks including in combin'a tion the steps of: contactinga lubricating oil distillate .with a selective solvent for aromatichydrocarbons, seg-- regating a lubricating oil extract phase,contacting. a

catalytic cycle oil with said lubricating oil extract phase,,

segregating a cycle oil extract phase, contacting a virgin gas oilincluding constituents boiling up to at least about process in whichcatalytically cracked products-boiling above about 430 F. are segregatedand contacted with a selective solvent for aromatic hydrocarbons forminga extract and raffinate phases, recycling hydrocarbons in said ratfinatephase to catalytic cracking and contacting a virgin gas oil fractionincluding constituents boiling up to at least about 1100 F. andcontaining metallic contaminan'ts with said extract phase, forming a gasoil extract phase and a gas oil raflinate phase substantially free ofmetallic contaminants, and passing hydrocarbons in said gas oilraflinate phase to catalytic cracking.

3. In the extraction of metal contaminants from a gas oil fractionincluding constituents boiling up to at least about 1100 F. by contactwith a selective solvent for aromatic hydrocarbons, the improvementwhich comprises contacting said gas oil fraction with spent selectivesolvent constituting the extract phase resulting from prior contact ofthe said selective solvent with hydrocarbons boiling above 430 F.selected from the group consisting of lubricating oil distillates andcycle oil, and recovering a gas oil raflinate phase substantially freeof metallic contaminants.

4. A method of extracting the metal contaminants from a straight runheavy gas oil fraction including constituents boiling up to at leastabout 1100 P. which comprises in combination contacting a lubricatingoil fraction with a selective solvent for aromatic hydrocarbons to formlube oil rafiinate and extract phases, segregating the lube oil extractphase and contacting the same with a cycle oil to form cycle oilrafiinate and extract phases, segregating the cycle oil extract phaseand contacting the same with said straight run heavy gas oil to formseparate gas oil raflinate and extract phases, said gas oil raflinatephase being substantially free of metallic contaminants and said gas oilextract phase containing metal contaminants from the heavy gas oil.

5. A combination catalytic cracking and extraction 14 process wherein astraight run heavy gas oil including constituents boiling up to at leastabout 1100 F. and containing metallic contaminants is employed as thecatalytic cracking feed stock which comprises in combination the stepsof contacting a lube oil fraction boiling above about 500 F. with aselective solvent for aromatic hydrocarbons to form lube oil extract andrafiinate phases, segregating the lube oil extract phase and contactingthe same with a cycle oil boiling above 430 F. from a catalytic crackingoperation to form separate cycle oil raflinate and extract phases,contacting the cycle oil extract phase with said straight run heavy gasoil to form separate gas oil raflinate and extract phases, said gas oilraflinate phase being substantially free of metallic contaminants andsaid gas oil extract phase containing metallic contaminants from saidstraight run gas oil, segregating the gas oil component of the gas oilraflinate phase and subjecting said component to catalyticcrack- 6. Aprocess as defined in claim 5 in which the cycle oil component of thecycle oil raflinate phase is segregated from rafiinate phase and iscatalytically cracked.

References Cited in the file of this patent UNITED STATES PATENTS'2,228,510 Dearbom et a1. Ian. 14, 1941' r 2,270,827 Tijmstra Jan. 20,1942 2,279,550 Benedict et a1 Apr. 14, 1942 2,342,888 I Nysewander et a1Feb. 29, 1944 2,374,102 Jahn' et al. Apr. 17, 1945 2,748,055 Payne May29, 1956

1. AN IMPROVED EXTRACTION PROCESS FOR THE PREPARATION OF CATALYSTCRACKING FEED STOCKS INCLUDING IN COMBINATION THE STEPS OF: CONTACTING ALUBRICATING OIL DISTILLATE WITH A SELECTIVE SOLVENT FOR AROMATICHYDROCARBONS, SEGREGATING A LUBRICATING OIL EXTRACT PHASE, CONTACTING ACATALYTIC CYCLIC OIL WITH SAID LUBRICATING OIL EXTRACT PHASE,SEGREGATING A CYCLE OIL EXTRACT PHASE, CONTACTING A VIRGIN GAS OILINCLUDING CONSTITUENTS BOILING UP TO AT LEAST ABOUT 1100*F. ANDCONTAINING METALLIC CONTAMINANTS WITH SAID CYCLE OIL EXTRACT PHASE, ANDSEGREGATING A GAS OIL RAFFINATE PHASE SUBSTANTIALLY FREE OF METALLICCONTAMINANTS.